No overlap in neurophysiological predictors of moment-to-moment fluctuations of behavioural variability and subjective attentional state

Behaviour fluctuates from moment to moment - often attributed to changes in subjective attentional states (e.g., mind wandering). Yet, it remains unclear how closely behavioural variability and subjective attentional state are related, and whether they share biological mechanisms. Using [~]2 hours of Metronome Response Task data, we combined magnetoencephalography, eye and head tracking, pupillometry, and thought probes to predict trial-to-trial fluctuations in both. Although they covaried weakly, this relationship was largely accounted for by time-on-task. Several markers including blink duration, pupil variability, and head movement predicted both measures. Dissociations also emerged: behavioural variability was linked to broadband functional connectivity and delta power, whereas off-taskness was predicted by theta, alpha, and beta power. Critically, predictive strength of behavioural variability and subjective reports were uncorrelated at the individual level, with substantial individual differences. For both outcomes, multimodal models outperformed univariate analyses. Our findings show that behavioural variability and subjective attentional state are largely dissociable, challenging the assumption that they share underlying process or that one causes the other.